Construction Industry Trends
October 2005
The Importance of Ventilation
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As energy prices continue to increase, the pressure is on the construction industry to continue developing energy-efficient buildings. However, while a tight building envelope often plays a key role in helping to reduce energy needs, it often does so at a cost—poor indoor air quality (IAQ). The solution? Ventilation.
Ventilation helps improve IAQ by reducing the concentration of pollutants in indoor environments, which often experience concentration levels two to five times higher than found outdoors. While passive ventilation—air moving on its own through open doors or windows—can help achieve this goal, energy conservation concerns limit its effectiveness. In most commercial buildings, windows are sealed and doorways protected to limit heating or cooling loss, while in homes, homeowners often keep windows and doors closed to save energy. That’s why active ventilation has become so important.
Active ventilation refers to any mechanical means of circulating air and exchanging indoor air with outdoor air. And unlike passive ventilation, active methods give builders and building owners greater control over ventilation, allowing them to adjust ventilation rates in order to meet acceptable IAQ requirements.
Ventilation, however, is much more complex than a simple matter of replacing bad air with good air. It’s ability to help improve IAQ depends on a number of factors, such as the number and types of pollutant sources in a building, the size of the building, and the needs of its occupants. That’s why, since 1973, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), has been publishing its own standard on ventilation.
When it first developed its ventilation standard, ASHRAE focused mainly on commercial buildings, believing that home owners were able to ensure adequate ventilation through passive means. But over time, the organization saw that tighter building envelopes in residential construction and the increasing evidence of the problems associated with indoor pollutants were making IAQ an important consideration both in homes and in public environments. That’s why, in 1997, ASHRAE chose to release its ventilation standard as two documents, with one designed for single-family homes and low-rise multi-family residences and one for commercial and institutional buildings.
While the goal of ASHRAE’s ventilation standards has always remained the same, its method of achieving this goal has changed. It now offers two approaches to ventilation: the ventilation rate procedure, which specifies minimum and recommended outdoor air flow rates, and the newer IAQ procedure, which rather than specifying ventilation rates, makes builders and building owners responsible for verifying that pollutant levels are held below the recommended limits.
ANSI/ASHRAE Standard 62.1-2004, Ventilation for Acceptable Indoor Air Quality, includes a number of changes to the previous edition, such as revisions to the ventilation rate procedure, the breathing zone ventilation rate, the IAQ procedure, and the minimum ventilation rate table. The standard also includes a new appendix that provides guidance on when the standard applies to new and existing buildings, as well as a code-intended language version that could be used by jurisdictions that have not adopted a building code.
The only nationally recognized indoor air quality standard developed solely for residences, ANSI/ASHRAE Standard 62.2-2004, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings, includes changes that make it more appropriate for residential applications. Recognizing the variety of residences that fall under the standards, as well as the types of different climates that may affect the buildings, the standard offers several alternatives to the recommendations it provides.
As with earlier editions of the standards, both have been approved by the American National Standards Institute (ANSI) as American National Standards. Standard 62.1 and 62.2 are also updated regularly, with new information added to the ASHRAE website in the form of addenda.
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